OOH! Something I can answer!
I routinely use bits as small as 0.011" (and 0.009" occasionally when the detail is needed) for engraving my designs on cribbage boards. They are just 2 flute end mills, not ball end carving bits, and with the smaller bits like 0.011", 0.010", 0.009" on darker woods they look almost like they were made with a laser.
Here are the bits I use (and quantity on hand - just in case I tuck a 10 pack away and forget where I put it):
Here is a mermaid being engraved using an 0.011" carbide end mill from drillman1.
Here is a longer video of the mermaid.
Pic 1 of the mermaid.
Pic 2 of the mermaid.
I had not cleaned out the lines yet, I took a pic as soon as it was done being carved.
Here is video of an old school Boeing totem logo being engraved.
Here is a pic of the logo.
The numbers and lines between the holes were done with an 0.0236" bit.
For the 0.015" - 0.009" bits I run them at:
20 IPM plunge
30 IPM feed
0.015" - 0.020" DOC
Two passes usually to get the depth of 0.030" - 0.040"
These were made on my original SO3 with a DeWalt router and PreciseBits “Ultra Precise” collet set. I now have an XXL and a water cooled 1.5KW ER-11 spindle and HDZ and in a couple of days will find out if the XXL cuts as well as the original smaller size SO3 with these bits.